Diaphragm pumps have been used for a wide variety of applications throughout the industries employing pumps. One type of such diaphragm pumps is a double diaphragm air-operated pump. This type of pump generally employs a sleeve and spool arrangement in the center section of the pump to control the directional flow of air to the diaphragm.
Historically, these pumps have used a high quality stainless steel to manufacture the sleeve and a hard anodized aluminum for the spool. The radial tolerance of these items is approximately 0.002 inches. Further it is necessary that the spool have a diameter that is only slightly less than that of the sleeve. This difference is generally about 0.0005 inches. Because of these strict tolerances, the sleeve and spool arrangements are generally assembled and kept as matched sets. The parts are not necessarily interchangeable from one set to another. Not only is the cost of high quality stainless and hard anodized aluminum quite high, but the manufacturing costs for machining these matched sets to the tolerances required are also very high.
The cost associated with these sleeves and spools would be livable if the items had an exceptionally long service life. However, the useable service life for these sleeve and spool arrangements is far less than desirable. For a variety of reasons, after a period of time in service the spool binds in the sleeve and requires more effort to move it back and forth until it reaches a point where it can no longer be moved, thus making the pump inoperable.
Therefore, it would be advantageous to provide a sleeve and spool arrangement which would not only cost less for the base material but be easier to manufacture and have a longer useful service life.